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package hostresolver
import (
"fmt"
"net"
"sort"
"strings"
"time"
"github.com/miekg/dns"
"github.com/patrickmn/go-cache"
"github.com/traefik/traefik/log"
)
type cnameResolv struct {
TTL time.Duration
Record string
}
type byTTL []*cnameResolv
func (a byTTL) Len() int { return len(a) }
func (a byTTL) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
func (a byTTL) Less(i, j int) bool { return a[i].TTL > a[j].TTL }
// Resolver used for host resolver
type Resolver struct {
CnameFlattening bool
ResolvConfig string
ResolvDepth int
cache *cache.Cache
}
// CNAMEFlatten check if CNAME record exists, flatten if possible
func (hr *Resolver) CNAMEFlatten(host string) (string, string) {
if hr.cache == nil {
hr.cache = cache.New(30*time.Minute, 5*time.Minute)
}
result := []string{host}
request := host
value, found := hr.cache.Get(host)
if found {
result = strings.Split(value.(string), ",")
} else {
var cacheDuration = 0 * time.Second
for depth := 0; depth < hr.ResolvDepth; depth++ {
resolv, err := cnameResolve(request, hr.ResolvConfig)
if err != nil {
log.Error(err)
break
}
if resolv == nil {
break
}
result = append(result, resolv.Record)
if depth == 0 {
cacheDuration = resolv.TTL
}
request = resolv.Record
}
hr.cache.Add(host, strings.Join(result, ","), cacheDuration)
}
return result[0], result[len(result)-1]
}
// cnameResolve resolves CNAME if exists, and return with the highest TTL
func cnameResolve(host string, resolvPath string) (*cnameResolv, error) {
config, err := dns.ClientConfigFromFile(resolvPath)
if err != nil {
return nil, fmt.Errorf("invalid resolver configuration file: %s", resolvPath)
}
client := &dns.Client{Timeout: 30 * time.Second}
m := &dns.Msg{}
m.SetQuestion(dns.Fqdn(host), dns.TypeCNAME)
var result []*cnameResolv
for _, server := range config.Servers {
tempRecord, err := getRecord(client, m, server, config.Port)
if err != nil {
log.Errorf("Failed to resolve host %s: %v", host, err)
continue
}
result = append(result, tempRecord)
}
if len(result) <= 0 {
return nil, nil
}
sort.Sort(byTTL(result))
return result[0], nil
}
func getRecord(client *dns.Client, msg *dns.Msg, server string, port string) (*cnameResolv, error) {
resp, _, err := client.Exchange(msg, net.JoinHostPort(server, port))
if err != nil {
return nil, fmt.Errorf("exchange error for server %s: %v", server, err)
}
if resp == nil || len(resp.Answer) == 0 {
return nil, fmt.Errorf("empty answer for server %s", server)
}
rr, ok := resp.Answer[0].(*dns.CNAME)
if !ok {
return nil, fmt.Errorf("invalid response type for server %s", server)
}
return &cnameResolv{
TTL: time.Duration(rr.Hdr.Ttl) * time.Second,
Record: strings.TrimSuffix(rr.Target, "."),
}, nil
}
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